Chapter 5 Evolution of Biodiversity

Earth is home to a tremendous diversity of species Ecosystem diversity- the variety of ecosystems within a given region. Species diversity- the variety of species in a given ecosystem. Genetic diversity- the variety of genes within a given species.

Species- a defined group of individuals that can interbreed with others of the same group and produce viable offspring. Scientist have named 2 million species, but believe there are about 10 million. Species richness- the number of species in a given area, used to get an approximate sense of biodiversity. Species evenness- the measure of whether a particular ecosystem is numerically dominated by one species or are all represented by similar numbers of individuals. Species richness of communities 1 and 2 is identical Community 1 is more evenly represented.

Determining Evolutionary relationships Phylogeny- diagram showing the evolutionary relationship of organisms. Relatedness is determined by similarity of traits. Morphology, behavior and genetics

Evolution is the mechanism underlying biodiversity Evolution- a change in the genetic composition of a population over time. Microevolution- evolution below the species level. Changes in the gene pool of a population over time. Macroevolution- Evolution on a grand scale… gives rise to new species or new genera, family, class or phyla.

Creating Genetic Diversity Genes- physical locations on chromosomes within each cell of an organism. Genotype- the complete set of genes in an individual. Mutation- a random change in the genetic code. Phenotype- the actual set of traits expressed in an individual. Can be environmentally influenced.

Evolution by artificial and natural selection Evolution by artificial selection- when humans determine which individuals breed. Evolution by natural selection- the environment determines which individuals are most likely to survive and reproduce.

Darwin’s theory of evolution by natural selection Individuals produce an excess of offspring. Not all offspring can survive. Individuals differ in their traits. Differences in traits can be passed on from parents to offspring. Differences in traits are associated with differences in the ability to survive and reproduce.

Natural Selection favors any combination of traits that improves and individuals fitness. Fitness- ability of an individual to survive and reproduce. Adaptations- traits that improve an individuals fitness

Evolution by Random Processes Mutation- occur randomly and can add to the genetic variation of a population. As mutations occur in the population, evolution occurs.

Evolution by Random Processes Genetic drift- change in the genetic composition of a population over time as a result of random mating. Non adaptive, random, particularly important in small populations.

Evolution by Random Processes Bottleneck effect- a reduction in the genetic diversity of a population caused by a reduction in its size. Examples- habitat loss, hunting, natural disaster or changes in the environment. Low genetic variation can lead to an increase risk of disease and low fertility Example: cheetah

Evolution by Random Processes Founder effect- a change in a population descended from a small number of colonizing individuals.

Speciation and extinction determine biodiversity Allopatric speciation- when new species are created by geographic or reproductive isolation.

Sympatric speciation- the evolution of one species into two species in the absence of geographic isolation, usually through the process of polyploidy, an increase in the number of sets of chromosomes. Polyploidy- the number of chromosomes increases to three, four, or even six sets. Seen in snails, salamanders, bananas, wheat, strawberries.

The pace of evolution Average global rate of evolution is one new species every 3 million years. Ability of a species to survive depends on how quickly it evolves the adaptations needed to thrive and reproduce under new conditions.

Evolution shapes ecological niches and determines species distributions Range of tolerance- all species have an optimal environment in which it performs well. The limit to the abiotic conditions they can tolerate is known as the range of tolerance. Fundamental niche- the ideal conditions for a species.

Niches Realized niche- the range of abiotic and biotic conditions under which a species lives. This determines the species distribution, or areas of the world where it lives. Niche generalist- species that live under a wide range of conditions. Niche specialist- species that live only in specific habitats.

The Fossil Record Fossils- remains of organisms that have been preserved in rock. Much of what we know about evolution comes from the fossil record.

The Five Global Mass Extinctions Mass extinction- when large numbers of species went extinct over a relatively short period of time.

The Sixth Mass Extinction Scientists feel that we are in our sixth mass extinction, occurring in the last two decades. Estimates of extinction rates vary widely, from 2 % to 25% by In contrast to previous mass extinctions, scientists agree that this one is caused by humans.